I use a corporate rate code (officialy given to me by my Travel Department) and in recent weeks I actualy have been carded by IC when I did not take out the corporate credit card. They wanted to see corporate id/business card.
A reservation I made in the IC BKK went to "contact IC" and when I called I was told that the RA upgrade on the corp rate will only be done if I bring ID.
I was also informed that not all IC's will upgrade on corp rate as some of them are just too discounted.